1. Field of the Invention
Embodiments of the invention relate to a permanently or temporarily implantable device comprising an elongated electric conductor.
2. Description of the Related Art
Such devices, for example electrode lines for electrostimulation and/or for picking up electronic signals, have the disadvantage that the electric conductor thereof may heat up in a nuclear magnetic resonance tomograph (also referred to as magnetic resonance imaging scanner) because the alternating magnetic fields present in the nuclear magnetic resonance tomograph induce quite significant electric currents in the electric conductor. Such induced currents can also be delivered to surrounding tissue by electrode poles of the electrode line and thus result in undesirable heating of tissue, for example. This heating may lastingly damage the body tissue and should be kept to a minimum. In comparison with conventional implants, the heating is to be reduced. For this reason, cardiac pacemaker patients today generally cannot be examined in a nuclear magnetic resonance tomograph, or only to a limited extent.
Typically, implantable cardiac pacemakers or defibrillators (hereinafter jointly referred to as cardiac stimulators or implantable pulse generators (IPG)) are connected at least to a stimulation electrode line that comprises a standardized electrical connection at the proximal end thereof provided for connection to the cardiac pacemaker or defibrillator, and that comprises one or more electrode poles at the distal end thereof provided for placement in the heart. Such an electrode pole is used to deliver electric pulses to the tissue (myocardium) of the heart or to sense electric fields, so as to be able to sense an activity of a heart as part of the sensing process. For these purposes, electrode poles typically form electrically conductive surface sections of an electrode line. Electrode poles are typically provided as annular electrodes in the form of a ring around the electrode line, or in the form of tip electrodes, at the distal end of the electrode line. The electrode poles are electrically conductively connected to contacts of the electric connection of the electrode line at the proximal end by way of one or more electric conductors. In this way, one or more electric conductors, which electrically connect one or more of the electrode poles to one or more of the contacts, run between the contacts of the electric connection of the electrode lines at the proximal end and the electrode poles at the distal end of the electrode line. These electric conductors can be used both to transmit stimulation pulses to the electrode poles and to transmit electric signals picked up by the electrode poles to the proximal end of the electrode line and will also be referred to as function lines hereinafter in the description. Such function lines are electric conductors that are required for the functions of the respective electrode line, and as such they are exposed to the risk that electric currents are induced in them by external alternating magnetic fields, which can lead, for example, to undesirable heating of the function lines or of the electrode poles connected thereto, or can lead to the delivery of currents to the surrounding tissue by way of the electrode poles, and thereby to heating of the surrounding tissue.